The present invention relates to printed circuit boards and more specifically, to a multilayer printed circuit board and a method for manufacturing such a printed circuit board constructed to increase the number of I.C. packages that can be mounted within a given surface area of the circuit board.
Multilayer printed circuit boards are formed of bounded stacks of cards or substrates of insulated material having tracks or lines of printed conductor elements located on their surfaces, the conductor elements being formed typically by the deposition of a metal such as copper on appropriate areas on the substrate or by etching away unwanted areas of a metal film such as copper which is bonded to the substrate. The card or substrate may be single or double sided, i.e., having lines of conductor elements on one or on both surfaces, respectively, of the card.
Prior printed circuit boards have been designed and manufactured with a different circuit on each card or substrate, the circuits being placed in overlying positions so that points for electrical connections between the circuits are congruent to each other. The individual circuits are then connected by drilling through the assembled cards and plating the holes thus formed with a layer of electrically conductive material such as copper. The leads of the circuit components are then mounted within the holes of the assembled board's exposed planar surface. These leads are then connected with conductor elements on different layers of the board. Each layer of conductor elements may be designed to provide different power supply potentials to the circuit or to be used for signal transmission. Samples of this type of construction may be found in U.S. Pat. Nos. 3,405,227, 3,830,956, 4,281,361, 4,438,560, 4,464,704, and 4,388,136. The layout of the conductor elements found in these patents along with the location of the circuit components vary from circuit board to circuit board. This results in a pattern of conductor elements which produces a high noise factor due to their lengths and their close proximity to a large number of other conductor elements. In addition, since the layout design of a high density circuit board is complex as a result of the intricate patterns of each conductor, together with their interconnecting points, it is a very time consuming and costly procedure to design such layouts.
It is therefore a principal object of this invention to provide a multilayer printed circuit board featuring domain areas or partitions which enable the circuit board to maintain better uniform heat and stress distribution while accommodating a high destiny of circuit components on the outer surface area of the board.
It is another object of this invention to provide a multilayer printed circuit board whose conductor elements are arranged so as to reduce and control the noise level in the circuit.
A further object to this invention is to provide a multilayer printed circuit board whose construction reduces the time for laying out the pattern on the various layers of the board.
A yet further object of this invention is to provide a method for producing a multilayer printed circuit board featuring the same areas or partitions which enable the circuit board to maintain better uniform heat and stress distribution while accommodating a high density of circuit components on the outer surface area of the board.
Another object of this invention is to provide a multilayer printed circuit board whose construction facilitates repair of the circuits without the need of expensive equipment to work into the inner layers of the board.